1. Field of the Invention
The invention relates to a support structure for a rotation body provided in a vehicle.
2. Description of the Related Art
In a vehicle, various rotation bodies are provided. Such a rotation body is supported in a housing so as to be rotatable around an axis of the housing by a rolling bearing including plural rolling elements provided between an outer race and an inner race. One example of the rotation body is a differential case provided in a differential device. As the rolling bearing, a conical roller bearing or an angular ball bearing is used. An appropriate preload needs to be applied to the conical roller bearing or the angular ball bearing in order (1) to position the rotation body in a radial direction and in an axial direction, (2) to provide sufficient rigidity of the bearing, and (3) to prevent vibration and resonance in the axial direction and the radial direction, and abnormal noise.
A method of adjusting the preload is well known, in which a shim is provided between the outer race of the bearing and the housing. There are variations in a space between the outer race of the bearing and the housing, due to machining tolerances of the outer race and the housing. Therefore, in the case where the preload is adjusted by providing the shim between the outer race of the bearing and the housing, several kinds of shims having different thicknesses are prepared, and a shim which is appropriate for the actual space between the outer race of the bearing and the housing is selected among the prepared several kinds of shims.
In this method, several kinds of shims need to be prepared. In addition, size of the space needs to be measured and the optimal shim needs to be selected in an assembly process. Therefore, a large number of components need to be prepared, and it takes much time to perform the assembly process.
For example, Japanese Patent Application Publication No. JP 2003-343692 A discloses that a disc spring is used, instead of the shim. In the case where the disc spring is used, even if there are variations in the space between the outer race of the bearing and the housing, the disc spring can always fill the space since an axial length of the disc spring can be increased and decreased. Therefore, only one kind of disc spring needs to be prepared, and therefore size of the space does not need to be measured during the assembly process.
However, in the case where the disc spring is used for adjusting the preload as in the Japanese Patent Application Publication No. JP 2003-343692 A, when a driving force is transmitted to the differential case, and accordingly the differential case is moved with respect to the housing in the axial direction, the disc spring may be plastically deformed. As a result, an appropriate preload may not be applied to the bearing. Also, the disc spring has a linear contact with the members between which the disc spring is provided. Therefore, when the differential case is repeatedly moved with respect the housing, the differential case, the housing, and the disc spring may be worn out.
The aforementioned problems may occur not only in the differential device, but also in other rotation bodies to which an appropriate preload needs to be applied, such as a counter shaft.